1. Field of the Invention
The disclosures herein generally relates to a surface emitting laser element and an atomic oscillator.
2. Description of the Related Art
A vertical cavity surface emitting LASER (VCSEL) is a semiconductor laser, which emits light in a direction perpendicular to a substrate surface. The VCSEL has a feature, compared with an end-face emitting type semiconductor laser, of low cost, of low power consumption, small size, high performance, and being easily integrated two-dimensionally.
The vertical cavity surface emitting laser has a resonator structure that has a resonator region including an active layer, and upper and lower Bragg reflection mirrors provided above and below the resonator region, respectively (See Japanese Published Patent Application No. 2008-53353). The resonator region has a predetermined optical thickness so that light with wavelength of λ resonates in the resonator region in order to obtain light with an oscillation wavelength of λ. The upper and lower Bragg reflection mirrors are formed by DBRs (Distributed Bragg Reflector) formed by laminating materials having different refraction indices, i.e. a low refraction index material and a high refraction index material, alternately. In the DBR, the low and high refraction index materials are formed so that optical thicknesses are λ/4 taking account of the refraction indices of the respective materials, in order to obtain high reflectance where the wavelength is λ.